Method for improving yield of sodium base greases



United States Patent lVIETHOD FOR IMPROVING YIELD OF SODIUM BASE GREASES James R. Roach, Beacon, Joseph F. Lyons, Wappingers Falls, and John P. Dilworth, Fishkill, N.Y., assignors to Texaco Inc., a corporation of Delaware No Drawing. Filed Sept. 8, 1955, Ser. No. 533,232

4 Claims. (Cl. 252-42) This invention relates to novel sodium base greases. More particularly, this invention involves the discovery that the yield of sodium base greases is substantially improved by the addition of the prescribed amount of estolide.

The novel grease compositions of this invention comprise an oleaginous lubricating base as the major component, a thickening agent which is a sodium soap of an organic compound selected from the group consisting of fatty acids containing at least 6 carbon atoms and hydroxy fatty acids containing at least 10 carbon atoms and an estolide of a hydroxy fatty acid containing 10 to 24 carbon atoms in an amount sufficient to increase the yield of the resulting sodium base grease. The estolide concentration which improves the yield of sodium base greases is between 1 and 3 weight percent. This invention also contemplates a method for increasing consistency of sodium base greases, i.e. changing a softer grade to a harder grade, by adding thereto 0.5 to 3 weight percent estolide.

The action of estolides in improving the yield is specific to sodium base greases. The addition of a l to 3 weight percent estolide actually decreased the yield of lithium base greases prepared by the high heat procedure which involves dehydration at a temperature about 400 F. and has substantially no effect upon lithium greases prepared by the low heat procedure, which involves dehydration at a temperature in the range of 310 to 330 F. In contrast, as will be shown hereafter, the addition of 1 to 3 weight percent estolide to the sodium base greases has a marked effect on the consistency of the grease.

It is obvious that the major advantage of this invention is that the cost of sodium base greases is substantially reduced. It is possible to prepare the desired grade of grease with substantially less soap which is the most expensive grease component. This reduction in cost is particularly noticeable when more expensive soap-forming components, such as myristic and l2-hydroxy stearic acid, are used as the soap precursors.

A second advantage is that grease compositions are formulated for the first time with the soaps of fatty acids containing less than 12 carbon atoms. Greases formulated with soaps of low molecular weight fatty acids have high melting points and are of particular interest at this time when lubricants usable for high temperatures in turbo-prop and turbo-jet aircraft are in demand.

Both fatty acids and hydroxy fatty acids are used in the formation of the sodium soap component of the greases of this invention. In addition to the conventional fatty acids from which sodium base greases are derived such as stearic acid, oleic acid, palmitic acid and their glycerides such as tallow, lard, etc., low molecular Weight acids such as myristic acid, lauric acid, capric acid, caprylic acid and caproic acid are usable as the soapforming component. In general, fatty acids, their monoesters and their glycerides, having 6 to 24 carbon atoms, are used to form the sodium soaps.

The hydroxy fatty acids, their monoesters and glycer:

"ice

ides requires a higher molecular weight when used as the soap precursor. As a consequence, 10 to 24 carbon atoms are required when the sodium soap is derived from a hydroxy fatty acid. These acids are preferably substantially saturated acids containing from 12 to 20 carbon atoms and one or two hydroxy groups, such as monoand di-hydroxy stearic, oleic, myristic and palmitic acids.

A particularly suitable material of this character is 12- hydroxy stearic acid. Other acids of this type which may be mentioned include 9- and 10-hydroxy stearic acids, 9,10-dihydroxy stearic acid, 8-hydroxy palmitic acid, and ll-hydroxy undecanoic acid.

The estolides, whose presence substantially improves the yield of sodium base greases, are intermolecular esters and polyesters, formed by the reaction of the hydroxy group of one molecule of a C to C hydroxy fatty acid with the carboxy group of another. The estolides of monohydroxy fatty acids containing 10 to 24 carbon atoms are represented by the formula:

wherein R is hydrogen or an aliphatic hydrocarbon radical containing from 1 to 21 carbon atoms, x is an integer having a valve of l to 22 and n is an integer having a valve of 2 to about 10. The average molecular weight of these estolides is in the range of 500 to 2500. The estolides of l2-hydroxy stearic acid are represented by the above formula wherein R is an alkyl radical containing 6 carbon atoms and x is equal to 10. The preferred estolides of l2-hydroxy stearic acid have an average molecular Weight in the range from about 800 to about 1,500.

The alkali metal salts of estolides are equivalent in function to the estolides themselves in hardening sodium base greases. The alkali metal salts are simply formed from the estolides by reaction with sufiicient alkali metal hydroxide to react with the free carboxyl group in the estolide. The sodium, potassium and lithium estolide salts may be used but the sodium salt is favored on the basis of cost.

The hardening of sodium base greases is effected with as little as 0.5 weight percent estolide, but estolide concentrations between 0.7 and 2.5 weight percent are usually employed. An upper limit of 3 weight percent is prescribed because softening of sodium base greases occurs with higher concentrations of estolide.

Grease hardening is obtained whether the estolide is added during grease manufacture or to the finished grease. Regardless of whether the estolide was added with the charge, after dehydration or to the finished grease on reheating to 320 F., substantial hardening of the grease as measured by the penetration at 77 F. is obtained. When the estolide is added to the finished grease, the estolide and grease mixture areheated to about 300 F. with stirring so as to effect uniform distribution of the estolide throughout the grease and subsequently cooled. Apparently, the present of the estolide has an effect on the formation and orientation of the soap fibers which permits the attainment of a given consistency with the use of much smaller amounts of soap than is possible in the absence of estolide.

Conventional grease-making procedures are employed for the manufacture of the novel greases of this invention. A recommended procedure involves mixing oleaginous lubricating base, the soap precursor, estolide, caustic soda and a small amount of water, saponifying this mixture at a temperature of about to 200 F. and dehydrating it at a temperature in the range of 270 to 320 F. after which the remainder of the oleaginous lubricating base is added during the stirred cooling of the grease. The ac.

tion of the estolide in increasing the yield of sodium base greases is not dependent on the grease-making procedure.

The grease compositions of this invention usually contain excess sodium hydroxide in an amount between 0.05 and 0.3 weight percent. The presence of the excess sodium hydroxide converts the estolide present in the grease mixtureto its sodium soap.

The action of estolides in improving yields is also observed in sodium soap greases containing organic thickening agents such as indigo. A sodium myristate-indigo grease having a synthetic ester as the major oil component has outstanding high temperature properties as disclosed in the copending, coassigned application Serial No. 423,240, filed April 14, 1954, now US. Patent No. 2,791,560, by I. P. Dilworth and James R. Roach. The addition of as little as 1 percent estolide to high temperature grease of this type substantially improves the grease yield.

The oleaginous lubricating base employed in the process of the invention for increasing the yield of sodium base greases is a hydrocarbon mineral lubricating oil, a synthetic lubricating oil prepared by cracking and polymerizing olefinic products or a synthetic lubricating base of the ester or ether type. Mixtures of hydrocarbon lubricating oils and synthetic lubricating oils can also be used as the oleaginous lubricating base. The hydrocarbon base mineral lubricating oils are most widely used as the oleaginous base, but synthetic ester-ether type lubricants are finding increasing use in specialty products designed for high and/or low temperature operation.

The mineral lubricating oils are paraffin, naphthene or mixed parafiin-naphthene base oils. The degree and amount of refining depends upon the particular purpose for which the grease is to be used. Solvent refining procedures such as furfural refining and solvent dewaxing with solvents such as methylethylketone-toluene mixtures are normally employed for the distillate and residual oils used in the invention. Broadly, hydrocarbon lubricating oil fractions having SUS viscosities at 100 F. about 50 to 1,100 are usable in the process of the invention.

The synthetic lubricating bases are usually of the ester or ether type. High molecular weight, high boiling liquid aliphatic dicarboxylic acid esters possess excellent viscosity-temperature relationships and lubricating properties and are finding ever increasing utilization in greases adapted for high and low temperature lubrication. Examples of this class of synthetic lubricating bases are the diesters of acids such as sebacic, adipic, azelaic, alkenylsuccinic, etc.; specific examples of these diesters are di- 2-ethylhexyl sebacate, di-Z-ethylhexyl azelate, di-Z-ethylhexyl adipate, di-n-amyl sebacate, di2ethylhexyl-ndodecyl succinate, di-Z-ethoxyethyl sebacate, di-2-methoxy-2-ethoxyethyl sebacate (the methyl carbitol diester), di-2-ethyl-2-n-butoxyethyl sebacate (the 2-ethylbutyl cellosolve diester), di-Z-n-butoxyethyl azelate (the n-butyl cellosolve diester) and di-2'-n-butoxy-2-ethoxy-ethyl-noctyl succinate (the n-butyl carbitol diester).

Polyester lubricants formed by a reaction of an aliphatic dicarboxylic acid of the type previously described, a glycol and a monofunctional aliphatic .monohydroxy alcohol or an aliphatic monocarboxylic acid in specified mol ratios are also employed as the synthetic lubricating base in the greases of this invention; polyesters of this type are described in US. 2,628,974. Polyesters formed by reaction of a mixture containing specified amounts of dipropylene glycol, sebacic acid and 2-ethylhexanol and of a mixture containing adipic acid, diethylene glycol and 2-ethylhexanoic acid illustrate this class of synthetic polyester lubricating bases.

Polyalkylene ethers as illustrated by polyglycols are also used as the lubricating base in the compositions of this invention. Polyethylene glycol, polypropylene glycol, polybutylene glycols and mixed polyethylene-polypropylene glycols are examples of this class of synthetic lubricating bases.

The sulfur analogs of the above-described diesters, polyesters and polyalkylene ethers are also used in the formulation of the grease compositions of this invention. Dithioesters are exemplified by di-Z-ethylhexyl thiosebacate and di-n-octyl thioadipate; polyethylene thioglycol is an example of the sulfuranalogs of the polyalkylene glycols; sulfur analogs of polyesters are exemplified by the reaction product of adipic acid, thioglycol and Z-ethylhexyl mercaptan.

The following examples demonstrate the greases of this invention whose yields are improved by the incorporation of the prescribed amount of estolide. The examples will show that this invention makes feasible products from greases of lower molecular weight fatty acids than was possible in the past.

EXAMPLE 1 A series of sodium laurate greases were prepared using an oil base comprising various ratios of a furfural refined, solvent dewaxed, paraffin base distillate oil having an SUS viscosity at F. of about 335 and of propane deasphalted, furfural refined, solvent dewaxed, clay contacted paraflin .base residuum having an SUS viscosity at 210 F. of 120. This series of sodium laurate greases all contained about 3 percent tricresyl phosphate as an EP additive and about 1 percent diphenyl-p-phenylenediamine as an oxidation inhibitor. The effect of an estolide of 12-hydroxy stearic acid having an average molecular weight of about 1600 on the hardness and grease yield of the sodium laurate greases is shown in Table I.

Table I.-Efiect of estolide on greases prepared from sodium soap The estolide is identified in the above table as being present in the composition in the form of sodium soap because it is converted to a soap by the excess sodium hydroxide.

It is evident from Table I that it is possible to substantially reduce the soap content of a sodium laurate grease and still obtain the same grade of grease by the use of as little as about 1 percent estolide. Approximately 24 percent soap is necessary to give a No. 2 grade grease in the absence of estolide, whereas as little as 13.6 percent soap can be used to obtain the same grade grease when 0.8 weight percent sodium soap of an estolide of 12-hydroxy stearic acid is prment.

The data in Table I also prove that the estolide can be present in the charge or can be added subsequent to dehydration of the soap mixture.

EXAMPLE 2 A sodium laurate grease was prepared having the following composition:

This sodium laurate grease had the following ASTM penetrations at 77 F.:

Unworked Worked The grease composition was then heated to about 320 F. and suflicient estolide added to give an estolide concentration of 0.9 weight percent. VThe estolide-containing grease was then cooled by stirring to give a harder grease having the following ASTM penetrations at 77 F.:

Unworked 200 Worked 320 The data in this example clearly prove that a yield improvement results from addition of a prescribed amount of estolide to a finished grease composition by simply reheating the same and incorporation of the estolide therein.

EXAMPLE 3 An effort was made to prepare greases firom the sodium soaps of capric, caprylic and caproic acid using a conventional procedure involving saponification at a temperature between 300 and 320 F. Using the residual oil-distillate oil mixture employed in Example 1 as the base oil, it was impossible to prepare greases in the absence of estolide with up to 30 percent soap. The addition of .2 to 2.5 weight percent estolide employed in Example 1 permitted the formation of a No. 0, 1 or 2 grade grease with less than 30% soap. The composition and properties of the resulting greases are shown in Table II wherein all of the products were formulated using a lubricating base comprising about 3 parts of the residual oil used in Example 1 and about 1 part of the distillate oil used in Example 1 and approximately 1 percent of diphenyl-p-phenylenediamine and about 3 weight percent tricresyl phosphate.

Table 11.-Tests n greases prepared from low molecular weight acids Sodium Soap:

Typo Caproate caprylate Oaprate Percent Sodium Soap 26. 6 25.0 28. 6 Estolide, percent 2.0 2.0 2.

162 287 176 333 372 294 Dropping Point, F 404, 408 346, 350 414,412

EXAMPLE 4 Two lithium myristate grease compositions were prepared by the same procedure involving dehydration of the soap base in approximately 15 percent of the base oil at a temperature of 400 F. The only substantial diiference between the two grease compositions was that one formulation contained 1.7 percent of an estolide of 12-hydroxy stearic acid having an average molecular weight of 1500. The composition and ASTM penetrations of these two grease compositions are shown in Table III.

Table III Calculated Compositions, percent:

Lithium myristate Excess LiOH Distillate Oil (Same as Example 1) Residual Oil (Same as Example 1) Diphenyl-p-pheuylenediamine Tricresyl phosphate Lithium soap of estolide of 12'hydroxy stearic acid ASTM Penetrations:

Unworked Wnrkari COCO It will be noted that the addition of estolide caused substantial softening of the lithium myristate grease. The estolide-free lithium myristate grease was essentially a No. 2 grade grease whereas the estolide-containing product was a 0 grade grease.

In Example 5 the action of estolide on sodium myristate greases is demonstrated. The improvement in yield is in striking contrast to the action of estolide on lithium myristate greases.

EXAMPLE 5 Two sodium myristate greases were prepared using as the base oil the same distillate oil-residual oil mixture used in Example 1. The only essential difference between the greases was that one contained 0.9 percent of an estolide of 12-hydroxy stearic acid having an average molecular weight of about 1500. The composition and ASTM penetrations of the two greases are shown in Table IV.

The presence of 0.9 weight percent estolide salt in the grease permitted formation of a No. 2 grade grease with 11.4 percent sodium myristate, whereas in the absence of the estolide, 18 percent sodium myristate was required to produce greases of equivalent hardness.

The effect of estolide on sodium myristate-indigo greases of outstanding high temperature properties, which are disclosed in the afore-identified application Serial No. 423,240, is shown in Example 6. The base oil used in this example comprises mainly a synthetic ester obtained by reaction of sebacic acid, 2-ethylhexane-1,3-diol and 2-ethy1hexanol in about a 2:1:2 ratio. A refined paratfin base distillate oil having an SUS viscosiity at F. of 330 constitutes a minor portion of the base oil composition.

EXAMPLE 6 Two sodium myristate-indigo greases were prepared by the procedure outlined in the afore-identified copending application. The only difference between the two greases was the presence of 1.3 weight percent of a sodium soap of an estolide of l2-hydr0xy stearic acid having an average molecular weight of about 1500. The composition and properties of the two greases are shown in Table V.

The data in the above table Show that the addition of an estolide to a sodium myristate-indigo grease substantially improves the yield. In the absence of estolide, approximately 20 weight percent of a 50-50 indigo-sodium myristate mixture was required to give a No. 1 grade grease, whereas only 11.2 weight percent of the same 50- 50 mixture was required to give a No. 2 grade grease when 1.3 weight percent of an estolide salt is present in the grease mixture.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for improving the yield of sodium base greases derived from fatty acids containing 6 to 24 carbon atoms, hydroxy fatty acids containing 10 to 24 carbon atoms, their glycerides and monoesters, and mixtures thereof, which comprises adding 0.5 to 3 weight percent of an estolide of a hydroxy fatty acid containing 10 to 24 carbon atoms to the finished grease composition, heating the mixture of estolide and finished grease to a temperature above 300" R, and cooling said estolide-grease mixture with the resulting formation of a harder grease composition.

2. A process according to claim 1 in which said estolide "has a molecular weight between 500 and 25 00 and the following general formula:

wherein R is selected from .the group consisting of hydrogen andan aliphatic hydrocarbon radical containing from 1 to 21 carbon atoms, x is an integer having a value of 1 to 22 and n is an integer having a value of 2 to about 10.

3. A process according to claim 1 in which said estolide has an average molecular weight from about 800 to 1500 and is derived from l2 hydroxy stearic acid.

4. A process according to claim 1 in which said estolide concentration is between 0.7 and 2.5 weight percent.

References Cited in the file of this patent UNITED STATES PATENTS 2,062,346 Zimmer et a1. Dec. 1, 1936 2,147,647 Gleason Feb. 21, 1939 2,628,938 Whitney Feb. 17, 1953 2,695,878 Entwistle Nov. 30, 1954 

1. A PROCESS FOR IMPROVING THE YIELD OF SODIUM BASE GREASES DERIVED FROM FATTY ACIDS CONTAINING 6 TO 24 CARBON ATOMS, HYDROXY FATTY ACIDS CONTAINING 10 TO 24 CARBON ATOMS, THEIR GLYCERIDES AND MONOESTERS, AND MIXTURES THEREOF, WHICH COMPRISES ADDING 0.5 TO 3 WEIGHT PERCENT OF AN ESTOLIDE OF A HYDROXY FATTY ACID CONTAINING 10 TO 24 CARBON ATOMS TO THE FINISHED GREASE COMPOSITION HEATING THE MIXTURE OF ESTOLIDE AND FINISHED GREASE TO A TEMPERATURE ABOVE 300*F., AND COOLING SAID ESTOLIDE-GREASE MIXTURE WITH THE RESULTING FORMATION OF A HARDER GREASE COMPOSITION. 